Andrea and Francesco,
...
The filters I'm talking about are the Ilford under the lens type. They are fine for most lenses but I don't think the system works with all size lenses, I've not measured the holder but I can if you're interested. They come with a holder and the filters can easily be put in and taken out making them ideal for split-grade printing. Some people have modified the holder so it accepts a Cokin filter ring that screws into the lens! Although you could always use the above the lens filters in one way or another.
And if you want electronics you can always add a RH Designs Analyser Pro!

Hi Martie,
thanks for your reply.

I've already saw this filter kit and I'm thinking to buy one to use with the CLS501.
I completely agree with you regarding the darkroom experience with a specific equipment but I've never tried a black and white head and I really would like to cop are it with my CLS.

Regarding the electronic heads you're right, they'll fail one day, so I'll get a VLS or the classic variopoint.
The variopoint should be the cheapest but it's a condensed head (the CLS and VLS are diffused from what I know) and I've red different kind of comments about condensed VS diffused.

If the VLS needs factors to be detremined with modern papers, why not do the same thing with the CLS that is already on the enlarger using M and Y filtration? Most papers come with tables for that in their data sheets which make nice starting points. This would safe a lot of money, trouble and time to make prints.